Telephone system



Dec. 4, 1934. Y J P. LOWE 1,983,477

TELEPHONE SYSTEM Filed Sept. 25, 1955 Patented Dec. 4, 1934 sense STATES PATENT OFFICE.

In Great Britain 7 Claims.

This invention relates to improvements in telephone systems, and has for its primary object to provide a transformer or inductance arrangement for use in such systems, the transformer arrangement being such that unwanted currents are balanced out. A further object of the invention is to provide an arrangement for use with a telephone fit up, to abolish or reduce side tone, i. e. the objectionable characteristic in telephone instruments of reproducing in the receiver sounds picked up by the transmitter of the same instrument. For example owing to .sidetone, it is difficult if not impossible to carry on a telephonic conversation in a noisy room.

Various methods have been employed in the past in an attempt to abolish or reduce .sidetone, nearly all of which have depended upon an accurate balance between the line and receiver fit-up.

With these and other objects in view, which will be clear from the following specification, my invention may be said to comprise one set of windings having a primary and associated secondary, the said secondary comprising two branches of equal inductance, in series, a second set of windings comprising two primary windings and associated secondary, the ends of the secondaries of the first set connected to the ends of the primary of the second set, the junction of the two secondary branches of the first set connected through the secondary of a transformer to the junction of the two primary windings of the second set forming a divided closed circuit, one branch of the'secondary of the first set divided into two windings arranged with respect to each other and their associated primary that current in the primary produces no effective current in this branch of the secondary and vice versa, currents induced in the secondary of the junction transformer by its primary dividing in the two components of the closed circuit, the primary of the first set inducing eifective currents in only one branch of the secondary.

In phone instruments a transformer arrangement comprises one set of windings having a primary connected to line, and associated secondary comprising two branches connected in series, a second set of windings comprising two primaries and associated secondaries, with receiver in cir- I cuit therewith, the ends of the two branches of the secondary of-the' first set connected to the ends of the two primary windings of the second set, the junction of the two branches of the sec ondary of the first set connected through a transformer secondary winding to the junction of the primary windings of the second set, the trans- September 30, 1932 mitting instrument in circuit with the primary of the junction transformer. One branch of the secondary of the first set is arranged so that currents in this branch are balanced out producing no current in the primary, and conversely currents in the primary produce no current in this branch, speech currents from line being impressed by one primary of the second set on the secondary thereby energizing the phone instrument currents, induced in the secondary of the junction transformer by the transmitter producing no current in the secondary of the second set but passing to line.

A preferred arrangement of my invention will now .be described with reference to the accompanying drawing, as applied to a telephone fit tip, for abolishing or reducing side tone.

Referring to, the drawing, in which like numerals and letters indicate like parts, Figure. 1 illustrates diagrammatically the subscribers system,and Figure 2 the operators system, these two systems being identical except for details as later described. Fig, 3 illustrates a simplified arrangement for a subscribers telephone; and, Fig. 4 illustrates an alternative receiver circuit. In Figure 1, aline transformer is provided, comprising four primary windings a, a a a and associated secondary windings, as, as as cs said windings being in cascade. One winding of the transformer such as as in the drawing is wound in the opposite sense with respect to the .others. One side of the line is connected to one e'ndof the combined primary winding, through condenser CB and the usual switch gear E associated with the receiver hook of the instrument and the other side is connected to the other end of the primary.

A second transformer D having two primaries d, d and associated secondaries ds, and ds is provided, the two primaries and two secondaries being connected in series. The ends of the combined primary windings d, d are connected to the ends of the combined windings as, cs cs (:8 forming a closed circuit, and the common junction of saidwindings d, al is connected to one side of the secondary winding as of a transformer C, which secondary as on the other side is connected to the four secondary windings as, (1.9 cs (18 Although only one winding as is shown it will be readily appreciated that other variations not afiecting the scope of the invention may be employed; for example more than one winding 0 may be employed. The secondaries ds, ds are connected to the receiver R.

One side of the line is connected through a bell coil 1) to one side of the microphone or transmitter T, the other side of which is connected to one side of the primary 0 of the transformer C. A condenser C. T. is shunted across the primary c, and the transmitter. The other side of the primary 0 is connected to one side of a second bell coil b the other side of which is connected to the other side of the line through the crutch hook contact E so that this circuit is energized when the receiver is lifted.

When sound Waves are'impressed on the diaphragm of the transmitter the choking action of the bell coils b, b confines the varying current to the primary c, transmitter and condenser. These varying currents are, however, induced into the secondary cs feeding a divided circuit, one half comprising secondaries as, as secondary es, and primary (1, the other half comprising secondaries as, as secondary cs, and primary d The coils a, al are arranged so that the two components of the divided current balance out, therefore no currents are induced in the associated secondaries as, ds and the receiver, which is connected across this combined secondary is therefore unaffected.

However owing to the fact that one coil, such as as of the transformer A is differential with respect to the others E. M. F.s in as and as are opposite and consequently speech currents will be induced into the combined primary winding by the other two coils as, as and pass to line.

Currents from the line pass through the primary coils a, a a a and owing to the fact that one coil as of this transformer A is differential no current is produced inone pair of secondaries cs 125 the current induced in the other pair passing through the secondary es and therefore one primary winding cl, thereby energizing the receiver. No currents will pass back to line through the secondary cs, owing to the choking effect of the bell coils b, b.

When the receiver is on the hook, normal line conditions prevail. When the subscriber is rung, ringing currents pass from the line via bell coil 1), condenser shunted across the coil cs, bell 'coil b crutch hook contact, and return to line.

The circuit for the exchange telephone illustrated in Figure 2, is similar except that the current is fed by means of a battery B. T. via a choke coil 2) to energize coil 0, and this figure will not be described, since its functioning is the same as that illustrated in Figure 1.

Variations, such as the transposition of transmitter and receiver transformers C and D respectively may be made. Also, in one arrangement each primary winding and its associated secondary may constitute a separate transformer, there being thus a number of independent transformers. In another arrangementsome or all of the windings of the input and other windings may constitute one transformer. Also, the ratio between primaries and secondaries is suitably arranged to produce desired step up or down, and the ratio between certain windings may be in such a ratio that side tone is not entirely eliminated. Thus one winding (1, may be tapped and the other winding 01 and the primary 0 connected to the tappings so that the amount of side tone can be controlled at will by the user, by varying the ratio between a, and (1 Referring to the drawing Fig. 3 illustrates a simplified arrangement for a subscribers telephone. In Fig. 3 two line transformers are provided. The first transformer comprises two primary windings a and a and two secondary windings as and as The second transformer has one primary winding 0 and one secondary winding cs. The transformer windings c, a, a and as are connected in series, but the windings c, a and a are shunted by a condenser by the operation of the switchhook contacts E when the receiver is lifted off the hook. When the receiver is normally resting on the switchhook the bell coils B in series with the condenser are across the line. The windings a and as are disconnected at switchhook E. The secondary windings as and cs are connected in such a manner that when speech is impressed on the transmitter T the currents induced in the said windings are in opposition and no sound is heard in the receiver R or the amount of sidetone desired by varying the tapping on the secondary cs. It will be appreciated that the number of windings on the transformer a and 0 may be varied, and may either be step up or step down.

One side of the line is connected to the windings as the other side of the line via the transmitter T to winding 0.

'When sound waves are impressed on the diaphragm of the transmitter, varying currents are set up which pass via windings c, a and a shunted by the condenser, currents are thereby induced into the secondary windings cs, as and as and the currents in the closed receiver circuit of es and as neutralize each other. The currents induced into the winding as pass to line.

Currents from the line pass through the coil as induce currents in the coils a, a and as. The

currents induced into the coils a and a pass via coil 0 transmitter and condenser, the currents induced into coil cs are in step with and assist the currents in coil as, incoming speech being heard in the receiver.

Fig. 4 illustrates an alternative method of connecting up the receiver circuit. The receiver being connected at one side to the centre point of union of the two coils, and on the other side to the ends of the two coils.

I claim:

1; In telephone systems, a transformer arrangement comprising one set of windings having a primary and associated secondary, the said secondary comprising two branches of equal inductance in series, a second set of windings comprising two primary windings and associated secondary, the ends of the secondary of the first set connected to the ends of the primary of the second set, the junction of the two secondary branches of the first set connected through the secondary of a transformer to the junction of the two primary windings of the second set,

'forming a divided closed circuit, one branch of the secondary of the first set divided into two windings arranged with respect to each other and their associated primary that current in the primary produces no effective current in this branch of the secondary and vice versa, currents induced in the secondary of the junction transformer by its primary dividing in the two components of the closed circuit, the primary of the first set inducing effective currents in only one branch of the secondary.

2. In telephone systems a transformer arrangement comprising one set of windings, comprising primary windings and associated secondary windings, the primary windings being arranged with reference to each other and to their associated secondary windings that currents in two adjacent primaries or adjacent secondary windings are balanced, a second set'of windings comprising two primary windings and associated secondaries, the ends of the combined windings of the secondary of the first set being connected with the outer ends of the primary windings of the second set, and the centre junction of the secondary windings of the first set being connected to the junction of the two combined primary windings of the second set through the secondary of a third transformer having an associated primary, whereby currents impressed on the primary windings of the first set produces current in the secondary of the second set, and currents impressed by the primary in the secondary of the junction transformer produces current in the primary of the first set, but no current in the two combined secondaries.

3. In phone instruments a transformer arrangement comprising, one set of windings having a primary connected to line, and associated secondary comprising two branches connected in series, a second set of windings comprising two primaries and associated secondary, with receiver in circuit therewith, the ends of the two branches of the secondary of the first set connected to the ends of the two primary windings of the second set, the jimction of the two branches of the secondary of the first set connected through a transformer secondary winding to the junction of the primary windings of the second set, the transmitting instrument in circuit with the primary of the junction transformer, one branch of the secondary of the first set arranged so that currents in this branch are balanced out producing no current in the primary, and conversely currents in the primary produce no current in this branch, speech currents from line being impressed by one primary of the second set on the secondary thereby energizing the phone instrument, currents induced in the secondary of the junction transformer by the transmitter producing no current in the secondary of the second set but passing to line.

4. A transformer arrangement according to claim 1, wherein the primary and secondary elements of the first set each comprises four windings, one of said elements having two branches of two windings each, one winding in one branch being arranged in opposite sense to the other winding in said branch, and the primary and secondary of the second set each comprising two windings in series.

5. A phone instrument as claimed in claim 3, wherein one side of the line is connected through a coil to the transmitter the other side of which is connected through the primary of the junction transformer to one side of a second coil which in turn is connected to line, the said coils choking back E. M. F.s produced by the transmitter and confining same to the circuit comprising transmitter, secondary of junction transformer and condenser shunted thereacross.

6. In a telephone system, side tone eliminating means comprising a first transformer having primary and secondary windings, the secondary being divided into two branches, one branch having two connected together balanced windings, a second transformer having two primary windings, a receiver in circuit with the secondary of said second transformer, the outer ends of the outer windings of the two branches of the secondary of the first transformer being connected with the outer ends of the primary windings of the second transformer, respectively, line wires connected with the primary of the first transformer, a third transformer having primary and secondary windings, a connection between one end of the secondary of said third transformer and the junction of the two primary windings of the second transformer, a connection between the other end of the secondary of the third transformer and the remaining ends of the two branches of the secondary of the first transformer, a transmitter connected at one side with one end of the primary winding of the third transformer and at its other side with one of the line wires, a coil in the last mentioned connection, a connection between the other end of the primary of the third transformer and the other line wire, and a coil in the latter connection.

7. A telephone system as set forth in claim 6 including a condenser shunting the transmitter and the primary winding of the third transformer.

J. P. LOWE. 

